Due to increase of gasoline price and greenhouse effect, people pay more attention to green industries. The green industries keep developing significantly. In recent year, technologies related to solar energy are improving in a very fast pace. Market main streams are silicon solar energy, thin film solar energy and concentrator photovoltaic (CPV) energy. Key parts of a concentrator photovoltaic module are Fresnel lens, III-V compound chips and the solar tracking system. Design thereof is very important to the efficiency of power generation. Concentrator photovoltaic energy system is used to focus solar energy by Fresnel lens so that the number of solar chips can be reduced. Meanwhile, better photoelectric conversion rate compared with that of conventional single crystal silicon, multi-crystal silicon or thin film solar cells can be available. The material used is polymethyl methacrylate (PMMA). The advantage is mature manufacturing process and cheap cost. However, this material can not withstand ultraviolet (UV) radiation so that it is easy to become yellow and reduce the ability to accept solar energy. Usually, life time of PMMA concentrators is about 3˜5 years. It is to say that power generation efficiency will soon reduce with time. In order to settle this issue, the best solution so far is to use a combination of silicone and glass (Silicone-On-Glass, SOG). Life time is estimated to be over 20 years. However, it is not easy for the combination of two materials to pass environment test. A commonly seen problem is peel-off. It causes the finished products useless after a period of time of use.
Silicone is mainly formed by the combination of silicon and oxygen. Average bonding energy (444 KJ/mol) of the combination is higher than that of carbon with carbon (356 KJ/mol) and carbon with oxygen (339 KJ/mol) in plastic materials, so the silicone can withstand high temperature. Silicone for optical use has high resistance against UV, and thus is not easy to become yellow. Furthermore, it can withstand high temperature. Therefore, it can be used in high temperature environments. It has low water absorption to endure high humidity. It has high light transmission. With respect to spectrum from ultraviolet to infrared light beams, the light transmission is better than other materials. It has high flowability, low viscosity and fast shaping features for mass production.
A prior art for manufacturing silicone glass condensing lens is to wash surface of a glass in advance and spread a primer on the glass. The primer is used to bond the glass and a silicone condensing lens. When the primer is ready to spread, the glass can be used to cover on a Fresnel lens mold filled with silicone. This is called imprinting method. Otherwise, the glass can cover a Fresnel lens mold which is not filled by silicone before silicone is injected to the space between the Fresnel lens mold and glass. This is injection molding. Then, silicone solidification process is performed. After the silicone is solidified completely and released, manufacturing of silicone glass condensing lens is finished.
However, there are still some problems for the conventional manufacturing method for glass condensing lens which need to be solved. First, adhesion between the glass and silicone is not good. It is easy to cause silicone to peel off when stripping, thereby damaging the Fresnel lens mold. Second, the primer is easy to react with air. Adhesion of the primer between the glass and silicone will decay along with time. Third, reaction temperature of the primer is high. Therefore, the Fresnel lens mold needs to use metallic materials to withstand high temperature baking. Cost of silicone glass condensing lens will increase.
A number of conventional ways for enhancing lens bonding are as follows.
Please refer to FIG. 1. A structure of solar battery package is disclosed. It is to cover a solar cell 1 with a top cladding layer 11 and a lower cladding layer 12 made of ethylene vinyl acetate (EVA) first. Then, a top layer 13 and a bottom layer 14 made of Celluloid and Teflon, respectively, form a structure composed of five layers. It has high degree of transparency so that the sunlight passes through easily. In addition, it has very desirable softness and flexibility, light weight and good strength characteristics. The aforementioned characteristics increase the usage of the solar battery module which, for example, can be used in solar energy vehicles. However, the prior art only discloses use of EVA as an adhesive. No improvement to increasing adhesion between the glass and the condensing lens is mentioned.
Please refer to FIG. 2. Another structure of solar battery package is disclosed. After the solar battery 21 is soldered, EVA material 22 is evenly spread in the solar cells 21. Later, the EVA material 22 surface is covered with low-iron glass 23. Then, it is embedded in a bracket 25 having a mattress 24 therebetween. However, like the structure of solar battery package mentioned above, the prior art only discloses EVA as an adhesive, and no improvement to increasing adhesion between the glass and the condensing lens is mentioned.
Please refer to FIG. 3. US Publication No. 2009-0277493 discloses an optoelectronic device 30. It has a solar cells 31 which has a surface smaller than a light entering surface 32 of the optoelectronic device 30; an optical unit 33 for focusing the sunlight onto a default area; and a transparent carrier 34. However, the invention doesn't disclose how to increase adhesion between the light entering surface 32 and the optical unit 33.
Please refer to FIG. 4. U.S. Pat. No. 5,211,761 discloses a method to increase adhesion between the substrate 41 (ceramic or quartz glass) and a polycrystalline silicon layer 43. It improves the adhesion therebetween by adding one or more adhesive layers 42 composed of silicone, silicide, cement, or silicon carbide between the substrate 41 and the polycrystalline silicon layer 43. However, the method for improving adhesion is not applied between the glass and a condensing lens.
This shows that the methods used in the industry to bond condensing lens and glass substrate still can not effectively solve the aforementioned disadvantages, causing poor production yield and high cost of silicone glass condensing lens. Thus, a simple and inexpensive method for bonding a condensing lens and a glass substrate at high operating temperature is desperately desired.